Question

#import <Foundation/Foundation.h>

typedef struct Node {
    int offset;
} Node;

int main (int argc, const char * argv[])
{

    @autoreleasepool {

        NSMutableArray *array = [[NSMutableArray alloc] init];
        Node node = {111111};
        NSValue *value = [NSValue value:&node withObjCType:@encode(Node)];
        [array addObject:value];

        NSValue *structValue = [array objectAtIndex:0];
        Node *n = (Node *)[structValue pointerValue];

        printf("offset: %d", n->offset);
    }
    return 0;
}

The code crashes on this line: printf("offset: %d", n->offset); but why?

Answer 1

The right way to get c-value back is getValue::

Node n;
[structValue getValue:&n];

pointerValue does not return a pointer to stored value, it reads a pointer value from memory where the Node is stored (like union { Node n; void* pointerValue; }).